Electrochemical cell having a cathode off a mixed phase metal oxide and method of preparation

ABSTRACT

The present invention is related to an electrochemical cell comprising an anode of a Group IA metal and a cathode of a mixed phase metal oxide prepared from a combination of starting materials comprising vanadium oxide and a mixture of at least one of a decomposable silver-containing constituent and a decomposable copper-containing constituent. The starting materials are mixed together to form a homogeneous admixture that is not further mixed once decomposition heating begins to form the product active material. The present cathode material is particularly useful for implantable medical applications.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application is a divisional application of Ser. No.09/439,872, filed Nov. 12, 1999, which is a continuation-in-partapplication of Ser. No. 08/917,072, filed Aug. 22, 1997, now abandoned.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention generally relates to the conversion ofchemical energy to electrical energy, and more particularly, to analkali metal electrochemical cell having a positive electrode comprisinga mixed phase metal oxide (MPO). Preferred mixed phase metal oxidesinclude silver vanadium oxide, copper vanadium oxide and copper silvervanadium oxide present in various phases or stoichiometric formulationsalong with a minor amount of the starting materials.

[0004] 2. Prior Art

[0005] Mixed metal oxides such as silver vanadium oxide are known foruse as cathode active materials in electrochemical cells. U.S. Pat. No.4,391,729 to Liang et al., which is assigned to the assignee of thepresent invention and incorporated herein by reference, describes amethod of preparing a composite cathode material by thermallydecomposing a vanadium salt such as ammonium metavanadate to producevanadium pentoxide.

[0006] The nitrate or the nitrite of a second metal is then added to thevanadium pentoxide, thoroughly mixed therewith and heated to dryness. Atthe end of the initial drying period, the mixture is again stirred andground to ensure homogeneity and subsequently baked for a minimum of 24hours at 360° C. During the final heating/decomposition period, nitrogenoxide gases are evolved, and at specific time intervals after evolutionof the nitrogen oxides, the admixture is stirred vigorously. The secondmetal is preferably selected from silver, copper, manganese and mixturesthereof. A typical product has the general formula Ag_(x)V₂O_(y) wherein“x” is in the range from about 0.5 to about 2.0, and “y” is in the rangefrom about 4.5 to about 6.0.

[0007] U.S. Pat. No. 5,516,340 to Takeuchi et al., which is assigned tothe assignee of the present invention and incorporated herein byreference, describes the preparation of a metal oxide composite cathodematerial such as copper silver vanadium oxide using various startingmaterials including vanadium oxide combined with the nitrate or thenitrite of a second and a third metal. The reactants are thoroughlymixed together and then baked. The baking protocol calls for a gradualincrease in the heating temperature up to a decomposition temperatureaccompanied by periodic stirring. A final grinding and heating steptakes place at 375° C. Further, U.S. Pat. No. 5,221,453 to Crespidescribes various silver vanadium oxide preparation techniques, forexample, milling powdered AgVO₃ or powdered Ag₂O with V₂O₅ and heatingat 520° C.

[0008] The metal oxide materials produced according to the techniquesdescribed by Liang et al., Takeuchi et al. and Crespi result in anelectrode active material, preferably a cathode active material, that isadvantageous for use in implantable medical devices such as animplantable cardiac defibrillator and the like where the battery powersource may run under a light, device monitoring load for extendedperiods of time interrupted by high rate pulse discharge during deviceactivation. However, during pulse discharge, the occurrence of voltagedelay is an undesirable characteristic of some metal oxide materials,which may result in a shortened implantable device life. There is,therefore, the need for a metal oxide cathode material that provides allthe advantages of the previously discussed metal oxide cathodematerials, but which additionally exhibits increased discharge capacityand decreased voltage delay for pulse discharge applications. Thepresent invention fulfills this need in a mixed phase metal oxidecathode material provided in a decomposition reaction wherein after thereactant starting materials or reactant constituents are initiallycombined into a homogeneous admixture, they are not further mixed duringdecomposition heating.

SUMMARY OF THE INVENTION

[0009] In lieu of preparation techniques calling for the mixing of thereactant constituents both before and during decomposition heating, thepresent invention is directed to mixed phase metal oxide activematerials synthesized from a homogenous admixture of starting materialsor reactant constituents that are not further mixed once decompositionheating begins. A homogeneous admixture is defined as a substantiallyidentical distribution of the reactant starting materials or reactantconstituents throughout the admixture prior to decomposition heating.The starting materials include both nitrate, nitrite, carbonate andammonium salt materials mixed with at least one metal oxide. Thus,although the ratio and type of starting materials does not differ fromthe standard preparation of silver vanadium oxide according to thepreviously discussed patent to Liang et al., the resulting mixed phasemetal oxide active materials have an increased ability for theintercalation and deintercalation of metal ions produced by oxidation ofthe anode while minimizing the detrimental effects of voltage delay.

[0010] Additionally, the present preparation techniques provide activematerials with increased energy density which is an unexpected result.

[0011] These and other aspects of the present invention will become moreapparent to those skilled in the art by reference to the followingdescription and to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a graph constructed from the differential thermalanalysis and thermal gravimetric analysis of silver nitrate.

[0013]FIG. 2 is a graph constructed from the differential thermalanalysis and thermal gravimetric analysis of a mixture of silver nitrateand vanadium oxide.

[0014] FIGS. 3 to 5 are graphs constructed from the discharge of lithiumcells having a mixed phase silver vanadium oxide cathode preparedaccording to the present invention in comparison to lithium cellsincorporating silver vanadium oxide synthesized according to the priorart decomposition preparation technique.

[0015]FIG. 6 is a graph constructed from the background voltages and P1minima voltages of a Li/MPO cell of the present invention, a Li/SVO cellof the prior art and a cell having 50% SVO/50% MPO.

[0016]FIG. 7 is a graph constructed from the background voltages and P4minima voltages of the cells used to construct the graph of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] An electrochemical cell including a mixed phase metal oxidesynthesized as an electrode active material such as a cathode activematerial according to the present invention preferably comprises ananode of a metal selected from Group IA of the Periodic Table of theElements. This group of metals is collectively referred to as the alkalimetals and comprises lithium, sodium, potassium, etc., and their alloysand intermetallic compounds including, for example, Li—Si, Li—Al, Li—Band Li—Si—B alloys and intermetallic compounds. The preferred anodecomprises lithium. An alternate anode comprises a lithium alloy, such asa lithium-aluminum alloy. The greater the amount of aluminum present byweight in the alloy, the lower the energy density of the cell.

[0018] The form of the anode may vary, but preferably the anode is athin metal sheet or foil of the anode metal, pressed or rolled on ametallic anode current collector, i.e., preferably comprising nickel, toform an anode component. In the exemplary cell of the present invention,the anode component has an extended tab or lead of the same material asthe anode current collector, i.e., preferably nickel, integrally formedtherewith such as by welding and contacted by a weld to a cell case ofconductive metal in a case-negative electrical configuration.Alternatively, the anode may be formed in some other geometry, such as abobbin shape, cylinder or pellet to allow an alternate low surface celldesign.

[0019] The electrochemical reaction at the cathode involves conversionof ions which migrate from the anode to the cathode into atomic ormolecular forms. The cathode material of the present invention comprisesat least a first cathode active constituent formed from readilydecomposable reactant constituent compounds consisting of metals fromGroups IB, IIB, IIIB, IVB, VB, VIB, VIIB, as well as from Group VIIIwhich are mixed together in a substantially homogeneous admixture andsubsequently thermally treated so as to effect the rapid preparation ofsuitable mixed phase metal oxide cathode materials. The thermaldecomposition heating occurs in an oxygen-containing atmosphere such asair or oxygen and at a temperature dictated by the constituent compoundsmaking up the admixture. Such decomposable reactant constituentsinclude, but are not limited to, those classes of compounds known asnitrates, nitrites, carbonates and ammonium salts. At such time as theheating temperature reaches the decomposition temperature of themixture, the mixture comprising the nitrates, nitrites and ammonium saltcompounds is characterized by the evolution of nitrogen oxide gas. Amixture containing carbonate compounds is characterized by the evolutionof carbon dioxide. The decomposable reactant compounds may also comprisea metal sulfide instead of the decomposable nitrates, nitrites andcarbonates.

[0020] Preferred mixed phase metal oxides are prepared by thoroughlymixing vanadium oxide with a metal, a metal oxide or a decomposablemetal compound of a second metal and possibly a third metal, wherein atleast one of the second and third metals are of a decomposable compound.Vanadium oxide is most preferredly in the form V₂O₅. This homogeneousadmixture, having a substantially identical distribution of the reactantconstituents throughout, is thereafter reacted in a thermaldecomposition reaction to form the resulting mixed phase metal oxide.The second and third metals are most preferably selected from silver,copper and manganese. An important aspect of the present invention isthat the substantially homogeneous admixture is not further mixed oncedecomposition heating commences. However, it should be pointed out thatthe mixture of the decomposable reactant constituent compounds can beheated and stirred or ground prior to the heating temperature reactingthe decomposition temperature without departing from the scope of thepresent invention.

[0021] Table 1 below lists a summary of thermal analysis data forvarious ones of the starting materials of the present invention. TABLE 1Decomposition Melting Point Starts Silver Nitrate 212° C. 444° C. SilverCarbonate 218° C. — (d.) Silver Nitrite 140° C. — (d.) Copper Nitrate114.5° C.   —HNO₃, 170° C. Copper Carbonate 200° C.-220° C. — ManganeseNitrate 25.8° C.  129.4°   Manganese Carbonate (d.) — Silver Sulfide(acanthite) tr. d. 175° C. Copper (II) Sulfide 103° C. 220° C.(covellite) (d.) Manganese Sulfide d. — Vanadium Oxide 690° C. 1,750°C.   Ammonium Metavanadate d. —

[0022] Table 2 below lists a summary of the thermal analysis data forvarious mixtures of the starting materials set forth in Table 1. TABLE 2Mole Melting Decomposition Ratio Point Starts Silver Nitrate + 1:1 207°C. 280° C. Vanadium Oxide Silver Carbonate + 1:1 190° C. — VanadiumOxide (d.) Silver Nitrite + 1:1 108° C. — Vanadium Oxide (d.) CopperNitrate + 1:1  82° C. 117° C. Vanadium Oxide Copper Carbonate + 1:1 287°C. — Vanadium Oxide (d.) Silver Nitrate, 1:1:1  82° C. ˜200° C.  CopperNitrate + Vanadium Oxide

[0023] A preferred mixed phase metal oxide according to the presentinvention is provided by thoroughly mixing silver nitrate with vanadiumpentoxide, which admixture is not further mixed once heating to thedecomposition temperature is reached.

[0024] Equation I below represents the heating of silver nitrate andvanadium oxide at about 207° C. when the silver nitrate material beginsto melt, but before the decomposition reaction.

At 207° C.: AgNO₃+V₂O₅→AgNO₃(liq)+V₂O₅  (I)

[0025] The decomposition of silver nitrate in a mixture with vanadiumpentoxide, with accompanying weight loss, begins at about 280° C., whichis a much lower temperature than the temperature at which pure silvernitrate decomposes, i.e., at about 444° C. The decomposition of silvernitrate results in the formation of silver vanadium oxide and NO_(x)gas.

[0026] Equation II below represents the decomposition reaction of silvernitrate and vanadium oxide at about 280° C.

At 280° C.: AgNO₃(liq)+V₂O₅→AgV₂O_(5.5)+NO_(x)  (II)

[0027] The preparation of silver vanadium oxide according to the presentinvention from a mixture of silver nitrate and vanadium oxide isillustrated in FIGS. 1 and 2. In FIG. 1 the melting point of silvernitrate is about 212° C., as indicated by the endotherm in thedifferential thermal analysis (DTA) curve 10. No weight loss is noted atthis temperature in the thermal gravametric analysis (TGA) curve 12.Weight loss begins at about 444° C., i.e., at commencement of thedecomposition reaction as evidenced by the evolution of NO_(x) gas,corresponding to the large endothermic transition in the silver nitrateDTA curve 10 at that temperature. The TGA curve 14 for a mixture ofsilver nitrate and vanadium pentoxide is shown in FIG. 2. This mixturemelts at about 207° C., as shown by the endothermic transition in theDTA curve 16 at this temperature.

[0028] According to the present invention, any one of the decomposablestarting materials are mixed together in a substantially homogeneousadmixture and subsequently thermally treated to provide the novel mixedphase metal oxide cathode active material. Thus, the present thermaldecomposition heating occurs in an oxygen-containing atmosphere and at atemperature of about 81° C. to about 290° C. depending on the startingmaterial constitutes. The exact temperature at which decompositionbegins is dictated by the starting materials. For a mixture of silvernitrate and vanadium oxide, mixing does not occur once the heatingtemperature reaches about 279° C. Mixing does not occur once a mixtureof silver carbonate and vanadium oxide reaches about 189° C. and for amixture of silver nitrite and vanadium oxide, once heating reaches about107° C. For a mixture of copper nitrate and vanadium oxide, all mixingceases once the heating temperature reaches about 81° C. and for coppercarbonate and vanadium oxide, once heating reaches about 286° C.

[0029] Those skilled in this art will readily recognize that variouscombinations of nitrates, nitrites, carbonates, sulfides and ammoniumsalts not listed in Table 2 are useful for preparation of mixed phasemetal oxides according to the present invention. These include, but arenot limited to, manganese nitrate and vanadium oxide; manganesecarbonate and vanadium oxide; manganese nitrite and vanadium oxide;silver sulfide and vanadium oxide; copper(II) sulfide and vanadiumoxide; manganese sulfide and vanadium oxide; silver nitrate, manganesenitrate and vanadium oxide; copper nitrate, manganese nitrate andvanadium oxide; silver carbonate, copper carbonate and vanadium oxide;silver carbonate, manganese carbonate and vanadium oxide; coppercarbonate, manganese carbonate and vanadium oxide; silver nitrate,copper nitrate and vanadium oxide; silver nitrate, manganese nitrite andvanadium oxide; copper nitrate, manganese nitrate and vanadium oxide;silver sulfide, copper(II) sulfide and vanadium oxide; silver sulfide,manganese sulfide and vanadium oxide; copper sulfide, manganese sulfideand vanadium oxide; silver sulfide, copper nitrate and vanadium oxide;silver sulfide, copper nitrite and vanadium oxide; silver sulfide,copper carbonate and vanadium oxide; silver nitrate, copper sulfide andvanadium oxide; silver nitrate, copper sulfide and vanadium oxide;silver carbonate, copper sulfide and vanadium oxide; silver sulfide,manganese nitrate and vanadium oxide; silver sulfide, manganese nitriteand vanadium oxide; silver sulfide, manganese carbonate and vanadiumoxide, and combinations and mixtures thereof.

[0030] Those skilled in the art will also understand that Table 2 liststhe various reactants in 1:1 mole ratios and their corresponding meltingpoint and decomposition temperature. However, the mole ratio can bechanged which will consequently change the melting point anddecomposition temperature of the resulting mixtures.

[0031] One preferred mixed phase metal oxide substantially comprises anactive material having the general formula SM_(x)V₂O_(y) wherein SM is ametal selected from Groups IB to VIIB and VIII of the Periodic Table ofElements and wherein x is about 0.30 to 2.0 and y is about 4.5 to 6.0 inthe general formula. By way of illustration, and in no way intended tobe limiting, one exemplary mixed phase cathode active materialsubstantially comprises silver vanadium oxide (SVO) having the generalformula Ag_(x)V₂O_(y) in at least one of its many phases, i.e., β-phasesilver vanadium oxide having in the general formula x=0.35 and y=5.18,γ-phase silver vanadium oxide having in the general formula x=0.74 andy=5.37 and ε-phase silver vanadium oxide having in the general formulax=1.0 and y=5.5, and combination and mixtures of phases thereof. In themixed phase metal oxide product, there may also be present a minoramount of the reactant constituents, particularly the decomposable metalcompound in a undecomposed state.

[0032] The preparation technique of a mixed phase metal oxide accordingto the present invention produces an active material displayingincreased capacity and decreased voltage delay in comparison toAgV₂O_(5.5) (SVO) prepared using a decomposition synthesis from AgNO₃and V₂O₅ starting materials, such as is disclosed in the previouslyreferenced U.S. Pat. No. 4,391,729 to Liang et al. The dischargecapacity and decreased voltage delay of the mixed phase metal oxide ofthe present invention is also an improvement over that of SVO typicallyprepared from Ag₂O and V₂O₅ by a chemical addition reaction such as isdescribed in U.S. Pat. No. 5,498,494 to Takeuchi et al., which isassigned to the assignee of the present invention and incorporatedherein by reference.

[0033] Advantages of the use of this mixed phase material includeincreased capacity and decreased voltage delay for pulse dischargeapplications. An example of such an application is the implantablecardiac defibrillator, where the battery may run under a light load forextended periods of time interrupted by high rate pulse discharge. Theoccurrence of voltage delay under these conditions is detrimental inthat it may shorten device life.

[0034] Another preferred mixed phase composite cathode material isprepared from a homogeneous admixture of vanadium oxide and a seconddecomposable metal compound, metal or metal oxide and a thirddecomposable metal compound, metal or metal oxide wherein at least oneof the second and third metal constituents is a decomposable form ofsilver and copper. According to the present invention, the homogeneousadmixture is formed from V₂O_(Z) wherein z≦5 combined with a mixture ofeither copper nitrate, copper nitrite or an ammonium salt of copper anda silver oxide or, a mixture of copper oxide and silver nitrate, silvernitrite or an ammonium salt of silver to provide the mixed phase metaloxide having the formula Cu_(x)Ag_(y)V₂O_(z) (CSVO), preferably with x≦y. In this preparation technique, the oxide starting materials mayinclude Ag₂O_(z) wherein z=2 to 1 and CuO_(z) wherein z=0 to 1. Thus,this composite cathode active material may be described as a metal-metaloxide-metal oxide, or a metal-metal-metal oxide and the range ofmaterial compositions found for Cu_(x)Ag_(y)V₂O_(z) is preferably about0.01≦x ≦1.0, about 0.01 ≦y ≦1.0 and about 5.01≦z ≦6.5. Anotherembodiment of the present invention has vanadium oxide combined withboth a decomposable compound of silver and copper. Typical forms of CSVOare Cu_(0.16)Ag_(0.67)V₂O_(z) with z being about 5.5 andCu_(0.5)Ag_(0.5)V₂O_(z) with z being about 5.75. U.S. Pat. Nos.5,472,810 to Takeuchi et al. and U.S. Pat. No. 5,516,340 to Takeuchi etal. describe the prior art preparation of CSVO.

[0035] The above described active materials are formed into an electrodefor incorporation into an electrochemical cell by mixing one or more ofthem with a conductive additive such as acetylene black, carbon blackand/or graphite. Metallic powders such as nickel, aluminum, titanium andstainless steel in powder form are also useful as conductive diluentswhen mixed with the above listed active materials. The cathode electrodefurther comprises a binder material which is preferably a fluoro-resinpowder such as powdered polytetrafluoroethylene (PTFE) or powderedpolyvinylidene fluoride (PVDF). More specifically, a preferred mixedphase cathode active material comprises SVO in any one of its manyphases, or mixtures thereof, and/or CSVO along with a minor amount ofthe decomposable reactants mixed with a binder material and a conductivediluent.

[0036] A preferred cathode active admixture comprises from about 80% to99%, by weight, of a cathode active material comprising either one orboth of the mixed phase SVO and CSVO materials prepared according to thedecomposition techniques of the present invention and mixed with asuitable binder and a conductive diluent. The resulting blended cathodeactive mixture may be formed into a free-standing sheet prior to beingcontacted with a current collector to form the cathode electrode. Themanner in which the cathode active mixture is prepared into afree-standing sheet is thoroughly described in U.S. Pat. No. 5,435,874to Takeuchi et al., which is assigned to the assignee of the presentinvention and incorporated herein by reference. Further, cathodecomponents for incorporation into an electrochemical cell may also beprepared by rolling, spreading or pressing the mixed phase cathodeactive mixture of the present invention onto a suitable currentcollector. Cathodes prepared as described above may be in the form ofone or more plates operatively associated with at least one or moreplates of anode material, or in the form of a strip wound with acorresponding strip of anode material in a structure similar to a“jellyroll”.

[0037] In order to prevent internal short circuit conditions, thecathode of the present invention is separated from the Group IA anodematerial by a suitable separator material. The separator is ofelectrically insulative material, and the separator material also ischemically unreactive with the anode and cathode active materials andboth chemically unreactive with and insoluble in the electrolyte. Inaddition, the separator material has a degree of porosity sufficient toallow flow therethrough of the electrolyte during the electrochemicalreaction of the cell. Illustrative separator materials include woven andnon-woven fabrics of polyolefinic fibers or fluoropolymeric fibersincluding polyvinylidine fluoride, polyethylenetetrafluoroethylene, andpolyethylenechlorotrifluoroethylene laminated or superposed with apolyolefinic or a fluoropolymeric microporous film. Suitable microporousfilms include a polytetrafluoroethylene membrane commercially availableunder the designation ZITEX (Chemplast Inc.), polypropylene membranecommercially available under the designation CELGARD (Celanese PlasticCompany, Inc.) and a membrane commercially available under thedesignation DEXIGLAS (C.H. Dexter, Div., Dexter Corp.). The separatormay also be composed of non-woven glass, glass fiber materials andceramic materials.

[0038] The electrochemical cell of the present invention furtherincludes a nonaqueous, ionically conductive electrolyte which serves asa medium for migration of ions between the anode and the cathodeelectrodes during the electrochemical reactions of the cell. Theelectrochemical reaction at the electrodes involves conversion of ionsin atomic or molecular forms which migrate from the anode to thecathode. Thus, nonaqueous electrolytes suitable for the presentinvention are substantially inert to the anode and cathode materials,and they exhibit those physical properties necessary for ionictransport, namely, low viscosity, low surface tension and wettability.

[0039] A suitable electrolyte has an inorganic or organic, ionicallyconductive salt dissolved in a nonaqueous solvent, and more preferably,the electrolyte includes an ionizable alkali metal salt dissolved in amixture of aprotic organic solvents comprising a low viscosity solventand a high permittivity solvent. The ionically conductive salt serves asthe vehicle for migration of the anode ions to intercalate or react withthe cathode active material. Preferably the ion-forming alkali metalsalt is similar to the alkali metal comprising the anode.

[0040] In a solid cathode/electrolyte system, the tonically conductivesalt preferably has the general formula MM′ F₆ or MM′ F₄ wherein M is analkali metal similar to the alkali metal comprising the anode and M′ isan element selected from the group consisting of phosphorous, arsenic,antimony and boron. Examples of salts yielding M′ F₆ are:hexafluorophosphate (PF₆), hexafluoroarsenate (AsF₆) andhexafluoroantimonate (SbF₆), while tetrafluoroborate (BF₄) is exemplaryof salts yielding M′ F₄. Alternatively, the corresponding sodium orpotassium salts may be used. Other inorganic salts useful with thepresent invention include LiClO₄, LiO₂, LiAlCl₄, LiGaCl₄, LiC(SO₂CF₃)₃,LiN(SO₂ CF₃)₂, LiSO₃F, LiB(C₆H₅)₄ and LiCF₃SO₃, and mixtures thereof.

[0041] Low viscosity solvents include tetrahydrofuran (THF), methylacetate (MA), diglyme, trigylme, tetragylme, dimethyl carbonate (DMC),1,2-dimethoxyethane (DME), diethyl carbonate and mixtures thereof, andhigh permittivity solvents include cyclic carbonates, cyclic esters andcyclic amides such as propylene carbonate (PC), ethylene carbonate (EC),acetonitrile, dimethyl sulfoxide, dimethyl formamide, dimethylacetamide, γ-butyrolactone (GBL) and N-methyl-pyrrolidinone (NMP) andmixtures thereof. In the present invention, the preferred anode islithium metal and the preferred electrolyte is 1.0 M to 1.2 M LiAsF₆ orLiPF₆ in PC/DME.

[0042] The preferred form of the electrochemical cell is a case-negativedesign wherein the anode/cathode couple is inserted into a conductivemetal casing such that the casing is connected to the anode currentcollector in a case-negative configuration, as is well known to thoseskilled in the art. A preferred material for the casing is titaniumalthough stainless steel, mild steel, nickel-plated mild steel andaluminum are also suitable. The casing header comprises a metallic lidhaving a sufficient number of openings to accommodate the glass-to-metalseal/terminal pin feedthrough for the cathode electrode. The anodeelectrode is preferably connected to the case or the lid. An additionalopening is provided for electrolyte filling. The casing header compriseselements having compatibility with the other components of theelectrochemical cell and is resistant to corrosion. The cell isthereafter filled with the electrolyte solution described hereinaboveand hermetically sealed such as by close-welding a stainless steel plugover the fill hole, but not limited thereto. The cell of the presentinvention can also be constructed in a case-positive design.

[0043] The following examples describe the manner and process ofmanufacturing an electrochemical cell according to the presentinvention, and they set forth the best mode contemplated by theinventors of carrying out the invention, but they are not to beconstrued as limiting.

EXAMPLE I

[0044] The synthesis of a mixed phase metal oxide (MPO) according to thepresent invention was accomplished using a homogeneous 1:1 mole ratio ofsilver nitrate (AgNO₃) and vanadium oxide (V₂O₅) reacted under an airatmosphere. The reaction was carefully controlled such that thereactants were only mixed prior to the thermal treatment of thematerial. Mixing or grinding of the components, as performed in thesynthesis of standard or prior art SVO, i.e. as described in thepreviously discussed U.S. Pat. No. 4,391,729 to Liang et al., wasexcluded once the heating step of the present preparation reach about279° C.

[0045] The resulting solid-state MPO product was used directly as theactive material for the cathode mixture without further preparation. TheMPO material was characterized by differential scanning calorimetry anddisplayed endothermic transitions at 466° C. 533° C. and 555° C. Thetransitions in the DSC curve indicate the presence of at least threemetal oxide phases: AgVO₃, AgV₂O_(5.5) (ε-phase), andAg_(0.74)V₂O_(5.37) (γ-phase). The existence of multiple phases is inagreement with the physical appearance of MPO, which is a mixture oforange particles with gray and brown particles.

EXAMPLE II

[0046] The MPO material prepared according to the present invention andSVO material prepared according to Liang et al. were incorporated intorespective alkali metal electrochemical cells. The MPO and SVO cellswere of a multiplate design using the respective cathode materialscontaining, by weight, 94% MPO or SVO, 3% polytetrafluoroethylene, 2%graphite, and 1% carbon black. The cathodes used Ti metal currentcollectors, and the total cathode surface area was about 80.6 cm².Lithium metal in contact with a Ni metal current collector was used asthe anode material. The cathodes were separated from the lithium anodeby a polypropylene separator. The cells were filled with 1M LiAsF₆ inPC/DME electrolyte and hermetically sealed.

[0047] All of the test cells were subjected to constant current pulsesof 1.5 Amps. The current pulses were applied in groups of four, eachpulse lasting 10 seconds in duration, with 15 seconds of rest betweenpulses. Three separate test regimes were used to simulate actual use ofthe battery in an implantable cardiac defibrillator device. The testregimes differed only in the time period between pulse trains and thevalue of the constant resistance load placed on the cells throughout thetest. In Test I, the cells were placed under a 17.4 kΩ load, and pulsedevery two months. Test II had the cells discharged under a 60.4 kΩ loadand pulsed every 4 months while Test III used a 100 kΩ load and thecells were pulsed every 6 months.

[0048] FIGS. 3 to 5 are graphs constructed from the results for theLi/MPO cells discharged under Tests I, II, III, respectively, incomparison to the results of the prior art Li/SVO cells discharged underthe same tests. In particular, in FIG. 3, curve 18 was constructed fromthe background voltage of the Li/MPO cell discharged according to TestI, curve 20 was constructed from the P1 min. voltage of that cell andcurve 22 was constructed from the P4 min. voltage. In comparison, inFIG. 3, curve 24 was constructed from the background voltage of theLi/SVO cell discharged according to Test I, curve 26 was constructedfrom the P1 min. voltage of that cell and curve 28 was constructed fromthe P4 min. voltage.

[0049] In FIG. 4, curve 30 was constructed from the background voltageof the Li/MPO cell discharged according to Test II, curve 32 wasconstructed from the P1 min. voltage of that cell and curve 34 wasconstructed from the P4 min. voltage. In comparison, in FIG. 4, curve 36was constructed from the background voltage of the Li/SVO celldischarged according to Test II, curve 38 was constructed from the P1min. voltage of that cell and curve 40 was constructed from the P4 min.voltage.

[0050] In FIG. 5, curve 42 was constructed from the background voltageof the Li/MPO cell discharged according to Test III, curve 44 wasconstructed from the P1 min. voltage of that cell and curve 46 wasconstructed from the P4 min. voltage. In comparison, in FIG. 5, curve 48was constructed from the background voltage of the Li/SVO celldischarged according to Test III, curve 50 was constructed from the P1min. voltage of that cell and curve 52 was constructed from the P4 min.voltage.

[0051] Voltage delay is indicated in these graphs by the occurrence ofP1 min. (minimum voltage of 1st current pulse) being lower than P4 min.(minimum voltage of 4th current pulse). As can be seen in FIGS. 3 to 5,the present invention Li/MPO cells displayed less voltage delay than thecomparable prior art Li/SVO cells, with this effect magnified as thetime period between administration of the respective pulse trainsincreased from Test I to Test III. In addition, the Li/MPO cellsprovided higher pulse minimum voltages than the Li/SVO cells, thusresulting in increased capacity and longer battery life.

EXAMPLE III

[0052] A second group of cells constructed according to Example I butcontaining various ratios of MPO and SVO was discharged under a protocolreferred to in house as three year accelerated discharge data (ADD). Thethree year ADD test consisted of placing the cells on a 60.4 kΩbackground load at 37° C, and pulsing the cells with a train once every120 days. The pulse train consisted of four 1.5 Amp pulses of 10 secondsduration with 15 seconds of rest between pulses. The three year ADD testreached conclusion after 52 months. Selected pulse train dischargeresults are presented in Table 3 with the complete discharge datagraphed in FIGS. 6 and 7. TABLE 3 Voltage (V) Cathode Bkgd V P1 min P4min PULSE TRAIN #5 100% MPO 2.744 2.353 2.366 50% MPO/50% SVO 2.7362.366 2.350 100% SVO 2.739 2.004 2.326 PULSE TRAIN #7 100% MPO 2.5571.811 2.117 50% MPO/50% SVO 2.556 1.781 2.095 100% SVO 2.554 1.485 2.008PULSE TRAIN #12 100% MPO 2.195 1.621 1.505 50% MPO/50% SVO 2.196 1.5481.455 100% SVO 2.195 1.257 1.119

[0053] In both FIGS. 6 and 7, the background voltage for the prior artLi/SVO cell is indicated by curve 54, the background voltage for the 50%SVO/50% MPO cell is indicated by curve 56 and the background voltage forthe Li/MPO cell is indicated by curve 58. FIG. 6 also shows therespective curves for P1 minima of those cells wherein curve 60 wasconstructed from the Li/SVO cell, curve 62 was constructed from the 50%SVO/50% MPO cell and curve 64 was constructed from the Li/MPO cell. TheLi/MPO cell performed better than the Li/SVO cell and the 50% SVO/50%MPO cell throughout the entire discharge life of the cells. In FIG. 7,the respective curves for P4 minima are shown for the tested cellswherein curve 66 was constructed from the Li/SVO cell, curve 68 wasconstructed from the 50% SVO/50% MPO cell and curve 70 was constructedfrom the Li/MPO cell. Again, the Li/MPO cell performed equal to orbetter than the other cells.

[0054] As is evident from Table 3 and FIGS. 6 and 7, the cellscontaining the MPO cathode material yielded much higher pulse voltagesthan the SVO control cells on long term test. This results in a cellwith significantly higher deliverable capacity.

[0055] It is appreciated that various modifications to the inventiveconcepts described herein may be apparent to those skilled in the artwithout departing from the spirit and the scope of the present inventiondefined by the hereinafter appended claims.

What is claimed is:
 1. A cathode for an electrochemical cell, thecathode formed by a process consisting essentially of the sequentialsteps of: a) forming a substantially homogeneous mixture of startingmaterials comprising vanadium oxide and at least one of a decomposablesilver-containing constituent and a decomposable copper-containingconstituent, wherein the homogeneous mixture is formed at a mixingtemperature below a decomposition temperature of the mixture of thestarting materials; b) heating the homogeneous mixture to itsdecomposition temperature without further mixing once heating to thedecomposition temperature begins; c) cooling the thusly produced mixedphase metal oxide; and d) contacting the mixed phase metal oxide to acathode current collector to form the cathode.
 2. The cathode of claim 1wherein the decomposable silver-containing constituent is selected fromthe group consisting of nitrates, nitrites, carbonates and ammoniumsalts.
 3. The cathode of claim 1 wherein the decomposablecopper-containing constituent is selected from the groups consisting ofnitrates, nitrites, carbonates and ammonium salts.
 4. The cathode ofclaim 1 wherein one component of the mixed phase metal oxide comprisesV₂O_(z) with z≦5.
 5. The cathode of claim 1 wherein the decompositiontemperature is at least about 81° C.
 6. The cathode of claim 1 whereindecomposition heating occurs in an oxygen-containing atmosphere.
 7. Thecathode of claim 1 wherein the mixed phase metal oxide substantiallyconsists of an active material having the general formula Ag_(x)V₂O_(y)and wherein 0.30≦x≦2.0 and 4.5≦y<6.0.
 8. The cathode of claim 1 whereinthe mixed phase metal oxide substantially consists of an active materialhaving the general formula Cu_(x)Ag_(y)V₂O_(z), and wherein 0.01≦x≦1.0,0.1≦y≦1.0 and 5.01≦z≦6.5.
 9. The cathode of claim 1 wherein the cathodefurther comprises at least one of a binder material and a conductiveadditive.
 10. A cathode for an electrochemical cell, the cathode formedby a process consisting essentially of the sequential steps of: a)forming a substantially homogeneous mixture of starting materialscomprising vanadium oxide and at least one of a decomposable salt ofsilver, copper, and manganese, wherein the homogeneous mixture is formedat a mixing temperature below a decomposition temperature of the mixtureof the starting materials; b) heating the homogeneous mixture to itsdecomposition temperature without further mixing once heating to thedecomposition temperature begins; c) cooling the thusly produced mixedphase metal oxide; and d) contacting the mixed phase metal oxide to acathode current collector to form the cathode.
 11. The cathode of claim10 wherein the decomposition temperature is at least about 81° C. 12.The cathode of claim 10 wherein the decomposition heating occurs in anoxygen-containing atmosphere.
 13. The cathode of claim 10 wherein themixed phase metal oxide substantially consists of an active materialhaving the general formula Ag_(xl V) ₂O_(y) and wherein 0.30≦x≦2.0 and4.5≦y≦6.0.
 14. The cathode of claim 10 wherein the mixed phase metaloxide substantially consists of an active material having the generalformula Cu_(x)Ag_(y)V₂O_(z), and wherein 0.01≦x≦1.0, 0.1≦y≦1.0 and5.01≦z≦6.5.
 15. A cathode active material for an electrochemical cell,the cathode active material formed by a process consisting essentiallyof the sequential steps of: a) forming a substantially homogeneousmixture of starting materials comprising vanadium oxide and at least oneof a decomposable silver-containing constituent and a decomposablecopper-containing constituent, wherein the homogeneous mixture is formedat a mixing temperature below a decomposition temperature of the mixtureof the starting materials; b) heating the homogeneous mixture to itsdecomposition temperature without further mixing once heating to thedecomposition temperature begins; c) cooling the thusly produced mixedphase metal oxide; and d) utilizing the mixed phase metal oxide as thecathode active material of the electrochemical cell.
 16. The cathodeactive material of claim 15 wherein the decomposable silver-containingconstituent is selected from the group consisting of nitrates, nitrites,carbonates and ammonium salts.
 17. The cathode active material of claim15 wherein the decomposable copper-containing constituent is selectedfrom the groups consisting of nitrates, nitrites, carbonates andammonium salts.
 18. The cathode active material of claim 15 wherein onecomponent of the mixed phase metal oxide comprises V₂O_(Z) with z ≦5.19. The cathode active material of claim 15 wherein the decompositiontemperature is at least about 81° C.
 20. The cathode active material ofclaim 15 wherein decomposition heating occurs in an oxygen-containingatmosphere.
 21. The cathode active material of claim 15 wherein themixed phase metal oxide substantially has the general formulaAg_(x)V₂O_(y) and wherein 0.30≦x≦2.0 and 4.5≦y≦6.0.
 22. The cathodeactive material of claim 15 wherein the mixed phase metal oxidesubstantially has the general formula Cu_(x)Ag_(y)V₂O_(y), and wherein0.01≦x≦1.0, 0.1≦y≦1.0 and 5.01≦z ≦6.5.